Properties of mortar and concrete containing fine sand contaminated with light crude oil

Properties of mortar and concrete containing fine sand contaminated with light crude oil

Sand contaminated with crude oil has become a major environmental concern worldwide. This problem poses threats to human health, the ecosystem, and the properties of the surrounding sand. Due to the prohibiting cost of the existing remediation methods, a more cost-effective way of utilizing oil contaminated sand is warranted. Mixing oil contaminated sand with cement and using this mix as alternative construction material is considered an innovative approach to reduce its environmental impact. This study is the first to investigate the effect of light crude oil on the physical and mechanical properties of fine sand, and mortar and concrete where contaminated sand is an ingredient. This approach is a critical step to sufficiently evaluate the suitability of this waste product as a sustainable building and construction material.

In the first stage, an extensive experimental study was conducted on the important geotechnical properties of fine sand contaminated with light crude oil. The results showed that water absorption, permeability, contact angle, frictional angle, and cohesion decreased with high levels of oil contamination. However, these properties of fine sand were enhanced at 1% oil contamination. The highest value of cohesion (10.76 kPa) and 10% enhancement in shear strength was observed at this oil contamination level. More importantly, the results of this stage provided information on the suitability of using this waste material as fine aggregates in mortar and concrete.

The second stage consisted of an evaluation of cement mortar properties containing fine sand contaminated with light crude oil. Mixing cement and water before adding the oil contaminated sand yielded up to 19% higher compressive strength compared to the cement mortar prepared by mixing the sand and cement before adding the water, due to a better reaction of cement particles and water during the hydration process. Similarly, curing in a fog room produced mortar of up to 45.6% higher compressive strength compared to mortars cured under other curing conditions, i.e. in water, in air, and in plastic bags. The scanning microscope observations revealed that cement mortars cured in the fog room had lower total porosity, smaller capillary pores, and denser calcium silicate hydrate compared to those cured under other methods. A w/c ratio of 0.5 was found to produce cement mortar with a higher compressive strength than mortar with a w/c ratio of 0.4 or 0.6. It was also found that the cement mortar with sand having more than 2% oil contamination requires a longer curing period to fully develop its compressive strength. The results of this stage demonstrated that proper mixing and curing methods, w/c ratio, and reasonable curing time are important for a cement mortar containing oil contaminated sand to achieve reasonable physical and mechanical properties for building and construction.

An investigation of the suitability of a geopolymer binder to produce mortar containing oil contaminated sand was investigated during the third stage. It was found that heat curing can increase the compressive strength of geopolymer mortar up to 54% compared to ambient curing situation. The geopolymer mortar with 1% of light crude oil contamination yielded a 20% higher compressive strength to mortar containing sand with a saturated surface dry condition. This was due to the high alkalinity of the solution, leading to the generation of more geopolymeric binder. Similarly, the formation of efflorescence decreased as the level of oil contamination decreased due to light crude oil filling up the pores. From this stage, it was demonstrated that geopolymer mortar containing oil contaminated sand has the potential as a new engineering material which has a positive impact on the environment.

An investigation of the properties of concrete containing oil contaminated sand was implemented as the last stage. The results of the investigation showed that the density of concrete deceased as the amount of crude oil increased due to an increase in the surface voids and total porosity. The highest compressive and splitting tensile strength was obtained for concrete with 1% of light crude oil contamination due to the oil optimising the sand cohesion. Above 1%, the bond between the cement paste and aggregates was affected, resulting in a decrease in strength properties. The developed simplified prediction equations to estimate the compressive strength of mortar and concrete containing fine sand contaminated with light crude oil gave a 98% accuracy between the experimental results and the predicted values.

An enhanced understanding of the behaviour of fine sand contaminated with light crude oil and the properties of mortar and concrete utilising this waste material
is the outcome of this investigation. This outcome will provide a benchmark for future studies and useful information to carefully consider oil contaminated sand for use in building and construction, and as a cost-effective alternative remediation method.